How can you Determination of Zinc (Zn+2) in solution
Determination of Zinc ion by Direct Titration using Eriochrome Black T as indicator
Zinc content in a sample can be determined quantitatively by complexometric
direct titration with EDTA at pH 10. The effective formation constant of the Zn-EDTA complex is ≥ 106 above pH 4. Eriochrome black T is used as an indicator; it is Blue when it is free (Hln2-) and wine-red when complexed with Zinc.
Initially, when the pH of the medium maintained at pH 7‒11, the Zinc ions
combine with indicator molecules to form Zn-indicator complex which appear as a winered color. Near the end point, EDTA breaks the Zn-indicator complexation, resulting in the formation of Zn-EDTA complex. Hence at the end point, the liberated free indicator yields a blue color to the solution.
1- Zinc ion solution (analyte)
2- pH10 buffer solution
3- Eriochrome black T indicator
4- 0.01 M EDTA solution
1- Pipette 25.0 mL of Zinc ion solution into a 250.0 mL conical flask and dilute to
about 200.0 mL with distilled water
2- Add 1 to 2 mL of pH10 buffer and 3 to 4 drops of Eriochrome Black T indicator to
3- Titrate with 0.01 M EDTA until the color changes from wine-red to pure blue.